Not applicable
1. Field of Invention
This invention relates to stethoscope chest pieces, specifically to such chest pieces, which are used in electronic stethoscopes.
Stethoscopes have not improved much in the past half-century, although they are often displayed as the symbol of medical care. There is much need for a more effective, inexpensive, easily carried sound amplifier to enable doctor or patient to monitor asthma, pneumonia, artery stenosis, valve leakage or heart rate irregularity. This invention claims a solution from classical sound physics and modern electronics. Resonant chambers mounted on a stereophonic stethoscope amplify body sounds as if in a theater, making them easily audible to both physician and patients, even in a thick-chested patient or through clothing.
This better sensing of clinically useful sounds enables better treatment in several ways. Resonant chamber stereophonic stethoscopes can be expected to be as useful and widely used by doctors, nurses and patients, as the current new devices for measuring blood pressure and temperature. Such an availability can bring earlier detection and treatment, which is a form of secondary prevention, in reducing the need for hospitalization and emergency rooms. Even primary prevention can be enhanced as patients pursue healthy living habits, while hearing for themselves the theater-like amplification of constricted breathing or brain blood flow, or the pounding and irregularity of an overstimulated heart.
2. Description of Prior art
It has long been known that the acoustic properties of stethoscopes can be modified with acoustic resonances that enhance heart sounds. For example, U.S. Pat. No. 4,200,169 (1980) to MacDonald, III et al. uses long acoustic resonance chambers built into the tubing that connect the chest piece to the binaural ear piece. Other attempts at improving the acoustic properties were made, when U.S. Pat. No. 4,633,971 (1987) to Robbins described a low-pass acoustic filter built into the stethoscope binaural tube.
Although this has indeed been of value, it was realized early that electronic amplification was also very useful, in addition to acoustic resonance amplification. U.S. Pat. No. 3,160,708 (1964) to Andries et al. describes a microphone chest piece with a simple conical sound pickup sitting on top of a transistorized amplifier. An improved modern version of this system was described in U.S. Pat. No. 5,548,651 (1996) to Long, whereby two sound pickup operated in stereo to send signals to each ear, separately. In that prior art, there is little effective reduction of ambient sound or satisfactory amplification of the valued 50-500 hz sounds. The sound pickups of these two patents were similar and consisted of metal bells feeding sound into sensitive microphones which were then connected to electronic amplification apparatus.
In all of these electronic stethoscopes there is a recurring issue of reducing the ambient noise picked up by the microphones, in addition to enhancing the natural frequencies of relevance in the examination of a patient. These chest pieces generally tend to be either isotropic in their sound sensitivity or with only a very small gain ( less than 6 dB) in the direction of the sound. Thus, they pick up almost as well the examination room noises as the chest sounds from the patient under examination. Sophisticated attempts have been made to cancel the noise coming from the examination room. Slavin, U.S. Pat. No. 4,438,772 (1982) subtracts the signal of one skin contact from the signal of another.
Later, U.S. Pat. No. 5,492,129 (1996) to Greenberger, claims two sound pickups proximal to each other, one being held to the patient and the other aimed at room noises. An electronic comparator is then claimed to eliminate the room noises by feeding the difference signal to the earpieces. Such schemes can be made to work but are extremely sensitive to small differences between the two sound pickups. Such differences are inevitable since the two pickups do not precisely amplify the room noises in the same way. This can be understood from the fact that one of them points to the patient and the other does not make contact with the patient, in order to decrease detection of patient sounds. Attempts can be made to compensate electronically for these differences, but the whole matter becomes very complex and very unreliable, as the examiner moves the pickups around the patient. This can often defeat the purpose of having a light-weight and reliable system for quickly examining patients without interference from room noises which are very often 40 or more dB stronger than the patient sounds of interest.
This invention relates to stethoscope chest pieces, specifically to such chest pieces, which are used for picking up sounds in electronic stethoscopes. In particular, a noise-reducing resonant chamber sound pick-up for electronic stethoscopes is claimed.
More specifically, a resonating chamber acoustically preamplifies the selected frequencies of heart sounds, 50-150 hz, and bruits of breath or blood, 150-500 hz, while rejecting ambient sounds. A skin contact has elastic foam support, whose rigidity is varied by varying the applied pressure, in order to select the preamplified band of sounds. The other side of the resonating chamber contains a sound transducer largely encased in heavy malleable metal that absorbs sound not coming from the chamber. The resulting superior signal-to-noise ratio permits two, small chambers to be used in a stereophonic chest piece little larger than that of a conventional stethoscope, with better amplification enabling examination through clothing even in heavy persons and also fitting into the carotid crease and rib spaces.
The main object of the invention is to detect patient sounds during a doctor examination, especially patient sounds that are relevant to medical diagnostics: such as being in the frequency band 50 to 150 hertz, for heart related sounds and being in the band 150 to 500 hertz for air and blood flow related sounds. The main advantage of the proposed invention is that this object is being accomplished in a compact, easily manufactured device that can be adapted to a wide variety of existing electronic stethoscopes, as well as other electronic diagnostic systems.
The second object of the invention is to reject examination room sounds, which are often as much as 40 or more dBs higher in intensity than the patient sounds. The advantage of the proposed invention is to do this in a way that allows a simple and compact electronic processing of the detected sounds. Another advantage is to do the sound rejection in a way that is independent of the details of the position of the sound pick-up around the patient body.
The third object of the invention is to select those patient sounds that are relevant to medical diagnostics, namely the heart sound band between 50 and 150 hertz, and the air and blood flow band between 150 and 500 hertz. The advantage of the present invention is that this frequency selection is done by very inventive simple acoustic means requiring no additional electronic processing. Yet, the selection mechanism allows the examiner the choice of changing the bands by changing the pressure applied by the hand on the pick-up during the examination, without having to relocate the pick-up on the patient.
A fourth object of the invention is to allow the pick-ups to be sufficiently compact that two of them can be used for accurate stereo placement in precision heart diagnostics. The advantage of the proposed invention is to allow for pickups that can be sufficiently close to each other that even infant heart diagnostics can be conducted, while also allowing the pick-ups to be placed at arbitrary locations on an adult patient.